This invention relates to a method for preparing modified starch products containing substituent groups comprised of anionic carboxyl groups having cationic amine groups bonded directly thereto. The invention also discloses a novel reagent useful in the modification of starches.
The modification by starch by chemical derivatization and, in particular, the preparation of starch ethers and esters is well known in the art. There are also a number of methods known for chemically modifying starches so as to produce amphoteric starch products containing both anionic and cationic substituent groups. Most of these prior art methods involve either an "in situ" formation of the amphoteric starch by simultaneous reaction of two different modifying agents with the starch or a multi-step procedure wherein the modifications of the starch are carried out in sequence. The latter procedure is exemplified in U.S. Pat. No. 3,751,422 wherein starch is reacted with an alkylene oxide, a nitrogen containing etherifying agent and a sultone in a sequential manner. In the resulting products, the anionic and cationic substitutent groups are bonded to different reactive sites on the starch molecule.
In contrast thereto, the amphoteric starch products of the present invention are produced by reaction directly with a novel reagent resulting in the production of starch products which are zwitterions, i.e. starches in which both the anionic and cationic substituent groups are bonded to the same reactive site on the starch molecule.